1. Field of the Invention
The present invention relates to a method of molding a ferrule and a mold therefor, and more particularly, to a method of molding a ferrule for an optical fiber connector, an optical fiber switch or the like, using plastic resin, and a mold therefor.
2. Description of the Related Art
Optical fibers of glass comprise a core having a diameter of 10 .mu.m, a cladding formed on an outer surface of the core and having a diameter of 125 .mu.m, and a protective cover of resin surrounding the cladding.
Ferrules for optical fiber connectors which connect both ends of optical fibers must be manufactured precisely to meet the ends of the optical fibers. The ferrules are formed by molding using a fluid plastic resin having a high temperature of approximately 180 degrees centigrade and employing a high injection pressure.
More specifically, as shown in FIG. 1, a ferrule 45A of a half of an optical fiber connector is provided with a plurality of fiber holes 42A into which a plurality of optical fibers 41A are inserted, and another ferrule 45B of the other half of the optical fiber connector has a structure same as the ferrule 45A. Two fitting pins 43 are inserted into pin holes 44A and 44B to integrate the halves, to thereby assemble the optical fiber connector. The optical connector is formed by inserting the optical fibers 41A and 41B into the fiber holes 42A and 42B and fixing the halves thereat by an adhesive.
The ferrules 45A and 45B of the optical fiber connector are produced by injection-molding or transfer-molding using plastic material. The mold for producing the ferrules 45A and 45B is comprised of a pair of molding ferrule halves which are openable and closable. Molding cores provided with pins for forming the fiber holes 42A and 42B and other pins for the pin holes 44A or 44B, are arranged in a cavity defined between abutting end faces of the molding ferrule halves, and are held and fixed thereat using the clamping force applied to the pair of molding ferrule halves. In this state, plastic resin is supplied into a cavity, resulting in the formation of desired ferrule 45A or 45B.
When holding and fixing the molding cores in place using the molding clamping force, it is necessary to firmly fix the molding cores from both the top and bottom sides without any clearance so as to precisely hold the molding cores at a fixed position without looseness.
However, when forming the ferrule 45A or 45B, plastic resin is supplied to the cavity at a high pressure of several hundred kg/cm.sup.2, for example, to reduce the shrinkage and deformation of the molding resin and to maintain a size. Therefore, to overcome the pressure due to the plastic resin, it is necessary to clamp the molding ferrule halves with a large molding clamping force of, for example, several tens of tons but, if this large mold clamping force is applied directly to the molding cores, the problem may occur of damage to the pins of the molding cores (Japanese unexamined publication No. 55-36809 published on Mar. 14, 1980).